A Kugelblitz is a black hole made of pure light. Such objects are only theoretical. Some laws of physics suggest that they should exist. Others suggest that in real life, a Kugelblitz could never actually form.
A black hole packs a tremendous amount of mass into a very small space. As a result, its gravity is so strong that not even light can escape it. All known black holes are made of matter.
But Einstein’s general theory of relativity says that matter and energy are two different forms of the same thing. (This is expressed in the famous equation E = mc2.) So in theory, a black hole could be made of dense energy — light — instead of matter. That would be a Kugelblitz, which means “ball lightning” in German.
But new research suggests that the laws of quantum physics would prevent a Kugelblitz from forming. According to quantum physics, when light gets too concentrated, something strange happens. Electrons and their antimatter partners (positrons) start to form.
Those particles can escape the region of concentrated light, taking energy with them. This will prevent the light from ever becoming concentrated enough to form a black hole. Even the superbright centers of active galaxies cannot produce light intense enough to cross this limit.